U.S. patent number 6,573,953 [Application Number 09/857,159] was granted by the patent office on 2003-06-03 for spatial light modulation device with a reflection type spatial light modulator and method.
This patent grant is currently assigned to Hamamatsu Photonics K.K.. Invention is credited to Yasunori Igasaki, Haruyoshi Toyoda, Narihiro Yoshida.
United States Patent |
6,573,953 |
Igasaki , et al. |
June 3, 2003 |
Spatial light modulation device with a reflection type spatial
light modulator and method
Abstract
In a spatial light modulation device using a reflection type
spatial light modulator, read light is a P-polarized light that
falls incident on the light reflection layer 17 at a slant. Liquid
crystal in the light modulation layer 17 is oriented so as to
incline, in association with the application of voltage by the
driving circuit 2, within a plane that is parallel to a normal
plane which includes the optical axes of both of the incident, read
light and the output, modulated light.
Inventors: |
Igasaki; Yasunori (Hamamatsu,
JP), Yoshida; Narihiro (Hamamatsu, JP),
Toyoda; Haruyoshi (Hamamatsu, JP) |
Assignee: |
Hamamatsu Photonics K.K.
(Shizuoka, JP)
|
Family
ID: |
18379244 |
Appl.
No.: |
09/857,159 |
Filed: |
May 31, 2001 |
PCT
Filed: |
December 03, 1999 |
PCT No.: |
PCT/JP99/06801 |
PCT
Pub. No.: |
WO00/34823 |
PCT
Pub. Date: |
June 15, 2000 |
Foreign Application Priority Data
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Dec 4, 1998 [JP] |
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10-345826 |
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Current U.S.
Class: |
349/25; 349/113;
349/114; 349/116; 349/130 |
Current CPC
Class: |
G02F
1/135 (20130101); G02F 1/13362 (20130101); G02F
1/1393 (20130101); G03H 2225/32 (20130101) |
Current International
Class: |
G02F
1/13 (20060101); G02F 1/135 (20060101); G02F
1/1335 (20060101); G02F 1/139 (20060101); G02F
001/135 (); G02F 001/133 (); G02F 001/133 (); G02F
001/133 () |
Field of
Search: |
;349/25,113,114,123,130,116 ;359/251,253,259,238,9
;382/211,298 |
References Cited
[Referenced By]
U.S. Patent Documents
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|
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4466702 |
August 1984 |
Wiener-Avnear et al. |
5130830 |
July 1992 |
Fukushima et al. |
5467216 |
November 1995 |
Shigeta et al. |
5555115 |
September 1996 |
Mitsuoka et al. |
5841489 |
November 1998 |
Yoshida et al. |
6348990 |
February 2002 |
Igasaki et al. |
6424388 |
July 2002 |
Colgan et al. |
|
Foreign Patent Documents
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0 023 796 |
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Feb 1981 |
|
EP |
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A 56-43681 |
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Apr 1981 |
|
JP |
|
A 4-178616 |
|
Jun 1992 |
|
JP |
|
Other References
J Gluckstad et al., "Lossless Light Projection", Optics Letters,
vol. 22, No. 18, 1997. .
Li et al., "Optically addressed phase-only spatial light modulator
using parallel-aligned nematic liquid crystal", Technical Report of
IEICE, LQE97-83, 1997-10..
|
Primary Examiner: Chowdhury; Tarifur R.
Attorney, Agent or Firm: Oliff & Berridge, PLC.
Claims
What is claimed is:
1. A spatial light modulation device, comprising: a light source
for outputting read light; and a reflection type spatial light
modulator, the reflection type spatial light modulator including a
light modulation layer having liquid crystal as light modulation
material, a light reflection layer, a light input surface
positioned at one side of the light modulating layer opposite from
the light reflection layer, and voltage application means for
applying an electric voltage to the light modulation layer, the
reflection type spatial light modulator receiving the read light at
the light input surface, transmitting the read light through the
light modulation layer, reflecting the read light off the light
reflection layer, and again transmitting the read light through the
light modulation layer, thereby performing light modulation in the
light modulation layer twice, and then outputting the modulated
light from the input surface, wherein the light source and the
reflection type spatial light modulator are arranged so that the
read light falls incident on the input surface following an input
optical axis that extends at a slant with respect to the light
reflection layer and so that the read light outputs from the input
surface following a reflection optical axis that extends at a slant
with respect to the light reflection layer, wherein the read light
includes approximately 100% P-polarized light component that has a
polarization direction within a normal plane which is defined to
include the input optical axis, the reflection optical axis, and a
normal line that extends normal to the light reflection layer, and
wherein the light modulation layer has liquid crystal molecules
which are oriented so that they are arranged, without any spiral
structure with respect to the normal line, within a plane
approximately parallel with the normal plane and so that they are
tilted, in association with application of the electric voltage by
the voltage application means, within the plane which is
approximately parallel with the normal plane, thereby causing no
twist between the liquid crystal molecules and an oscillating plane
of the P-polarized light component of the read light.
2. A spatial light modulation device as claimed in claim 1, wherein
the read light includes 100% P-polarized light component, and the
light modulation layer has the liquid crystal molecules which are
oriented so that they are arranged, without any spiral structure
with respect to the normal line, within a plane parallel with the
normal plane and so that they are tilted, in association with
application of the electric voltage by the voltage application
means, within the plane which is parallel with the normal plane,
thereby causing no twist between the liquid crystal molecules and
the oscillating plane of the read light.
3. A spatial light modulation device as claimed in claim 1, wherein
the liquid crystal molecules in the light modulation layer are
processed into a homogeneous orientation.
4. A spatial light modulation device as claimed in claim 1, wherein
the liquid crystal molecules in the light modulation layer are
processed into a homeotropic orientation.
5. A spatial light modulation device as claimed in claim 1, further
comprising a Fourier transform lens for spatially Fourier
transforming the modulated light which is outputted from the
reflection type spatial light modulator.
6. A spatial light modulation device as claimed in claim 1, wherein
the voltage applying means includes a photoconductive layer
controlling the electric voltage applied to the light modulating
layer in accordance with write light incident thereto.
7. A spatial light modulation device as claimed in claim 1, wherein
the light modulation layer modulates, in association with
application of the electric voltage by the voltage application
means, phase of the P-polarized light component of the read light,
without rotating the oscillating plane of the P-polarized light
component of the read light.
8. A spatial light modulation method, comprising the steps of:
preparing a reflection type spatial light modulator, the reflection
type spatial light modulator including a light modulation layer
having liquid crystal as light modulation material, a light
reflection layer, a light input surface positioned at one side of
the light modulating layer opposite from the light reflection
layer, and voltage application means for applying an electric
voltage to the light modulation layer, the reflection type spatial
light modulator being for receiving read light at the light input
surface, transmitting the read light through the light modulation
layer, reflecting the read light off the light reflection layer,
and again transmitting the read light through the light modulation
layer, thereby performing light modulation in the light modulation
layer twice, and then outputting the modulated light from the input
surface; and inputting the read light to the reflection type
spatial light modulator in a manner that the read light falls
incident on the input surface following an input optical axis that
extends at a slant with respect to the light reflection layer and
that the read light outputs from the input surface following a
reflection optical axis that extends at a slant with respect to the
light reflection layer, wherein the read light includes
approximately 100% P-polarized light component that has a
polarization direction within a normal plane which is defined to
include the input optical axis, the reflection optical axis, and a
normal line that extends normal to the light reflection layer, and
wherein the light modulation layer has liquid crystal molecules
which are oriented so that they are arranged, without any spiral
structure with respect to the normal line, within a plane
approximately parallel with the normal plane and so that they are
tilted, in association with application of the electric voltage by
the voltage application means, within the plane which is
approximately parallel with the normal plane, thereby causing no
twist between the liquid crystal molecules and an oscillating plane
of the P-polarized light component of the read light.
9. A spatial light modulation method as claimed in claim 8, wherein
the read light includes 100% P-polarized light component, and the
light modulation layer has the liquid crystal molecules which are
oriented so that they are arranged, without any spiral structure
with respect to the normal line, within a plane parallel with the
normal plane and so that they are tilted, in association with
application of the electric voltage by the voltage application
means, within the plane which is parallel with the normal plane,
thereby causing no twist between the liquid crystal molecules and
the oscillating plane of the read light.
10. A spatial light modulation method as claimed in claim 8,
wherein the liquid crystal molecules in the light modulation layer
are processed into a homogeneous orientation.
11. A spatial light modulation method as claimed in claim 8,
wherein the liquid crystal molecules in the light modulation layer
are processed into a homeotropic orientation.
12. A spatial light modulation method as claimed in claim 8,
further comprising a method of using a Fourier transform lens to
spatially Fourier transform the modulated light which is outputted
from the reflection type spatial light modulator.
13. A spatial light modulation method as claimed in claim 8,
wherein the voltage applying means includes a photoconductive layer
controlling the electric voltage applied to the light modulating
layer in accordance with write light incident thereto.
14. A spatial light modulation method as claimed in claim 8,
wherein the light modulation layer modulates, in association with
application of the electric voltage by the voltage application
means, phase of the P-polarized light component of the read light,
without rotating the oscillating plane of the P-polarized light
component of the read light.
Description
TECHNICAL FIELD
The present invention relates to a spatial light modulation method
and a spatial light modulation device that uses a spatial light
modulator with liquid crystal as the light modulation material, and
particularly to a spatial light modulation method and, a spatial
light modulation device that uses a reflection type spatial light
modulator.
BACKGROUND ART
There are two types of spatial light modulators: intensity
modulation types and phase modulation types. Many spatial light
modulators are the intensity modulation type, which are used in
liquid crystal televisions, projector light bulbs, and the like. On
the other hand, the phase modulation types show promise in fields
such as light information processing and hologram processing. This
is because the phase modulation types differ from intensity
modulation types in that they have high light usage efficiency. A
system that uses a phase modulating type spatial light modulator is
disclosed by J. Gluckstad et al. in "Lossless Light Projection",
OPTICS LETTERS, Vol. 22, No. 18, 1997.
Phase modulation type spatial light modulators include reflection
types and transmission types. Reflection type spatial light
modulators differ from transmission types in that the same surface
serves as the light input surface for the read light and the light
output surface for the modulated light. For this reason, normally
the modulated light is separated from the read light using a half
mirror. However, as a result, there is a problem in that light
usage efficiency drops. The benefit of using a phase modulation
type is lost.
DISCLOSURE OF THE INVENTION
It is an objective of the present invention to take the
above-described problem into account and provide a spatial light
modulation method and a spatial light modulation device that uses a
reflection type spatial light modulator and that has high light
usage efficiency.
In order to overcome the above-described problem and other
problems, the present invention provides a spatial light modulation
device, comprising: a light source for outputting read light; and a
reflection type spatial light modulator, the reflection type
spatial light modulator including a light modulation layer having
liquid crystal as light modulation material, a light reflection
layer, a light input surface positioned at one side of the light
modulating layer opposite from the light reflection surface, and
voltage application means for applying an electric voltage to the
light modulation layer, the reflection type spatial light modulator
receiving the read light at the light input surface, transmitting
the read light through the light modulation layer, reflecting the
read light off the light reflection layer, and again transmitting
the read light through the light modulation layer, thereby
performing light modulation in the light modulation layer twice,
and then outputting the modulated light from the input surface,
wherein the light source and the reflection type spatial light
modulator are arranged so that the read light falls incident on the
input surface following an input optical axis that extends at a
slant with respect to the light reflection layer and so that the
read light outputs from the input surface following a reflection
optical axis that extends at a slant with respect to the light
reflection layer, wherein the read light includes approximately
100% P-polarized light component that has a polarization direction
within a normal plane which is defined to include the input optical
axis, the reflection optical axis, and a normal line that extends
normal to the light reflection layer, and wherein the light
modulation layer has liquid crystal molecules which are oriented so
that they are arranged, without any spiral structure with respect
to the normal line, within a plane approximately parallel with the
normal plane and so that they are tilted, in association with
application of the electric voltage by the voltage application
means, within the plane which is approximately parallel with the
normal plane, thereby causing no twist between the liquid crystal
molecules and the oscillating plane of the P-polarized light
component of the read light.
According to the spatial light modulation device of the present
invention with this configuration, the read light falls incident on
the input surface of the reflection type spatial light modulator at
a slant. Accordingly, it is possible to separate, without using a
half mirror, the read light inputted to the reflection type spatial
light modulator from the read light reflected from the reflection
type spatial light modulator. Accordingly, light usage efficiency
can be increased and the freedom of arrangement of the input and
output optical systems can be increased.
Additionally, according to the present invention, read light that
includes approximately 100% P-polarized light component falls
incident on the input surface at a slant. The P-polarized light
component of the read light has a polarization direction within the
normal plane that includes the normal line of the light reflection
layer of the spatial light modulator and the input optical axis of
the read light. Also, the liquid crystal in the light modulation
layer is oriented so that they tilt, in association with
application of voltage, within the plane that is substantially
parallel with the normal plane. Accordingly, no twist develops
between the P-polarized light component of the read light and the
arrangement direction of the liquid crystal molecules. For this
reason, only phase modulation is attained, without any rotation of
the polarization plane.
Because the same is for the reflected light, the polarization plane
of the modulated light that is finally outputted from the
reflection type spatial light modulator has the same polarization
plane with that of the input light. Accordingly, the modulated
light includes approximately 100% P-polarized light component, and
is outputted. It is possible to maintain a high diffraction
efficiency.
In particular, it is desirable that the read light may include 100%
P-polarized light component, and the light modulation layer may
have the liquid crystal molecules which are oriented so that they
are arranged, without any spiral structure with respect to the
normal line, within a plane parallel with the normal plane and so
that they are tilted, in association with application of the
electric voltage by the voltage application means, within the plane
which is parallel with the normal plane, thereby causing no twist
between the liquid crystal molecules and the oscillating plane of
the read light.
In this case, no twist occurs between the P-polarized read light
and the arrangement direction of the liquid crystal molecules.
Accordingly, phase-only modulation can be attained without any
rotation of the polarization plane. Accordingly, an extremely high
diffraction efficiency can be maintained.
It is desirable that the liquid crystal in the light modulation
layer be processed in the homeotropic or homogeneous orientation.
By processing the liquid crystal in the homeotropic or homogeneous
orientation, the liquid crystal molecules are aligned within a
predetermined plane with no spiral structure. By aligning this
predetermined plane approximately with the normal plane, it is
possible to perform phase modulation without any rotation of the
polarization plane.
According to another aspect, the present invention provides a
spatial light modulation method, comprising the steps of: preparing
a reflection type spatial light modulator, the reflection type
spatial light modulator including a light modulation layer having
liquid crystal as light modulation material, a light reflection
layer, a light input surface positioned at one side of the light
modulating layer opposite from the light reflection surface, and
voltage application means for applying an electric voltage to the
light modulation layer, the reflection type spatial light modulator
being for receiving read light at the light input surface,
transmitting the read light through the light modulation layer,
reflecting the read light off the light reflection layer, and again
transmitting the read light through the light modulation layer,
thereby performing light modulation in the light modulation layer
twice, and then outputting the modulated light from the input
surface; and inputting the read light to the reflection type
spatial light modulator in a manner that the read light falls
incident on the input surface following an input optical axis that
extends at a slant with respect to the light reflection layer and
that the read light outputs from the input surface following a
reflection optical axis that extends at a slant with respect to the
light reflection layer, wherein the read light includes
approximately 100% P-polarized light component that has a
polarization direction within a normal plane which is defined to
include the input optical axis, the reflection optical axis, and a
normal line that extends normal to the light reflection layer, and
wherein the light modulation layer has liquid crystal molecules
which are oriented so that they are arranged, without any spiral
structure with respect to the normal line, within a plane
approximately parallel with the normal plane and so that they are
tilted, in association with application of the electric voltage by
the voltage application means, within the plane which is
approximately parallel with the normal plane, thereby causing no
twist between the liquid crystal molecules and the oscillating
plane of the P-polarized light component of the read light.
In particular, it is desirable the read light may include 100%
P-polarized light component, and the light modulation layer may
have the liquid crystal molecules which are oriented so that they
are arranged, without any spiral structure with respect to the
normal line, within a plane parallel with the normal plane and so
that they are tilted, in association with application of the
electric voltage by the voltage application means, within the plane
which is parallel with the normal plane, thereby causing no twist
between the liquid crystal molecules and the oscillating plane of
the read light.
Also, it is desirable that the liquid crystal in the light
modulation layer be processed in the homogeneous or homeotropic
orientation.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a configurational view of a spatial light modulation
device according to a first embodiment of the present
invention.
FIG. 2 is a view showing configuration of a reflection type spatial
light modulator used in the spatial light modulation device of FIG.
1.
FIG. 3A is an explanatory perspective view for explaining
arrangement of liquid crystal in a light modulation layer of the
spatial light modulator of FIG. 2.
FIG. 3B is a cross-sectional view taken along line IIIB--IIIB of
FIG. 3A.
FIG. 3C is an explanatory perspective view for explaining change in
alignment of liquid crystals in the light modulation layer of FIG.
3A in accordance with application of voltage.
FIG. 3D is a cross-sectional view taken along line IIID--IIID of
FIG. 3C.
FIG. 4 is a configurational view showing arrangement of a
comparative example of a spatial light modulation device.
FIG. 5A is an explanatory perspective view for explaining alignment
of liquid crystals in the light modulation layer of the spatial
light modulator of the comparative example of FIG. 4.
FIG. 5B is a cross-sectional view taken along line VB--VB of FIG.
5A.
FIG. 5C is an explanatory perspective view for explaining change in
alignment of liquid crystals in the light modulation layer of FIG.
5A in association with application of voltage.
FIG. 5D is a cross-sectional view taken along line VD-5D of FIG.
5C.
FIG. 6 is a graph showing results obtained in a first experiment
that measured diffraction efficiency of the arrangement of the
first embodiment.
FIG. 7 is a graph showing results obtained in the first experiment
that measured diffraction efficiency of the arrangement of the
comparative example.
FIG. 8 is an explanatory view for explaining how to change
orientation of the spatial light modulator and polarization
direction of the read light in a second experiment, in order to
change the ratios of P- and S-polarized light components.
FIG. 9 is a graph showing results of the second experiment that
measured diffraction efficiency obtained at different P- and
S-polarized light component ratios.
FIG. 10 is a configurational view showing a laser processing device
using the spatial light modulation device of the first
embodiment.
FIG. 11 is a configuration view showing an optical interconnection
device configured by applying the spatial light modulation device
of the first embodiment.
FIG. 12A is an explanatory perspective view for explaining
orientation of liquid crystals in the light modulation layer of a
reflection type spatial light modulator according to a second
embodiment.
FIG. 12B is a cross-sectional view taken along line XIIB--XIIB of
FIG. 12A.
FIG. 12C is an explanatory perspective view for explaining change
in alignment of liquid crystal in the light modulation layer of
FIG. 12A.
FIG. 12D is a cross-sectional view taken along line XIID--XIID of
FIG. 12C.
BEST MODE FOR CARRYING OUT THE INVENTION
Next, preferred embodiments of the present invention will be
described while referring to the attached drawings. It should be
noted that in order to facilitate understanding of the description,
like components in the drawings will be provided with the same
reference numbering to the degree possible and redundant
explanation omitted.
First, a spatial light modulation device according to a first
embodiment of the present invention will be described based on
FIGS. 1 to 11.
FIG. 1 is a schematic view showing configuration of a spatial light
modulation device according to the present: embodiment.
As shown in FIG. 1, a spatial light modulation device, 100 includes
a reflection type optically addressed spatial light modulator
(referred to as SLM, hereinafter) 1. The SLM 1 includes a light
modulation portion 1A, a light address portion 1B, and a mirror
layer 15 provided between the light modulation portion 1A and the
light address portion 1B. The light address portion 1B has a write
light input surface 1b for receiving inputted write light. The
light address portion 1B changes optical characteristics of the
light modulation portion 1A in accordance with the inputted write
light. The light modulation portion 1A includes a read light input
surface 1a for receiving inputted read light. The light modulation
portion 1A modulates the inputted read light according to the
changes in the optical characteristics. The light modulation
portion 1A again modulates the read light after the read light
reflects off the mirror layer 15, and then outputs the modulated
light from the read light input surface 1a.
The SLM 1 is arranged in a three-dimensional XYZ space with the
orientation shown in FIG. 1. That is, assuming that the direction
perpendicular to the surface of the sheet of FIG. 1 is the X
direction and the surface of the sheet is the YZ plane, the SAM 1
is arranged so that the line extending normal to the reflection
layer 15 and to the read light input surface 1a extends in the Z
axial direction.
A light source 3, a transmission type liquid crystal television 5,
and an imaging lens 6 are disposed to the side of the write light
input surface 1b of the SLM 1. The light source 3 is for generating
the write light. The transmission type liquid crystal television 5
is for displaying write light images. The imaging lens 6 is for
imaging the image signals, which are included in the write light,
on the write light input surface 1b of the SLM 1. An electric
signal generator 4 is connected to the transmission type liquid
crystal television S. The electric signal generator 4 is for
controlling display of the write light images.
On the other hand, a He--Ne laser 7, a lens 8, a spatial filter 9,
and a collimator lens 10 are disposed on the write light input
surface 1a side of the SLIM 1: The He--Ne laser 7, the lens 8, the
spatial filter 9, and the collimator lens 10 are disposed along an
input optical axis I. The input optical axis I is tilted from the
line Z, which is normal to the reflection layer 15 and to the input
surface 1a, in the Y direction by an angle .theta.
(0.degree.<.theta.<90.degree.). The He--Ne laser 7 serves as
a light source for generating the read light.
Also, a Fourier transform lens 30 is disposed along an output
optical axis O. The output optical axis O is tilted in the Y
direction by the same angle .theta.
(0.degree.<.theta.<90.degree.), but to the opposite side of
the normal line Z than the input optical axis I. Accordingly, the
YZ plane, which includes all of the input optical axis I of the
read light, the reflection optical axis O of the read light, and
the line Z normal to the input surface 1a and to the reflection
layer 15 of the SLM 1, is defined as a "normal plane" for the read
light.
The He--Ne laser 7 is for emitting linearly-polarized read light.
The He--Ne laser 7 is disposed with an orientation (referred to as
a "laser predetermined reference position," hereinafter) so that
the Ne--Ne laser 7 emits, as the linearly-polarized read light, a
P-polarized light whose electric field oscillation direction is
parallel with the normal plane (YZ plane).
Next, the configuration of the SLM 1 will be described in detail
with reference to FIG. 2.
The SLM 1 of the present embodiment is a parallel-aligned
nematic-liquid-crystal spatial light modulator (PAL-SLM).
The SLM 1 has a glass substrate 12 formed with an AR
(anti-reflection) coat layer 11 for preventing unnecessary
reflection of incident write light. The AR coat layer 11 defines
the write light input surface 1b. An ITO (indium tin oxide) layer
13 and a photoconductive layer 14 are deposited on the surface of
the glass substrate 12 opposite the AR coat layer 11. The
photoconductive layer 14 is formed from amorphous silicon (a-Si).
The resistance of the amorphous silicon changes in accordance with
intensity of light incident thereto. The optical address portion 1B
is configured from the AR coat layer 11, the glass substrate 12,
the ITO 13, and the photoconductive layer 14. A dielectric
multi-layer film mirror layer 15 is accumulated on the surface of
the photoconductive layer 14 that is opposite from the ITO 13.
The SLM 1 further has a glass substrate 21. An AR coat layer 22 for
preventing unnecessary reflection of incident read light is formed
on a surface of the glass substrate 21. The AR coat layer 22
defines the read light input surface 1a. An ITO (indium tin oxide)
layer 20 is deposited on the surface of the glass substrate 21 that
is opposite the AR coat 22.
Alignment layers 16 and 19 are formed on the mirror layer 15 and
the ITO 20, respectively. The alignment layers 16, 19 are disposed
facing each other, and are connected by a frame-shaped spacer 18.
The inside of the frame of the spacer is filled with nematic liquid
crystal, which forms a liquid crystal layer 17 that serves as a
light modulation layer. The ITOs 13 and 20 are connected to a drive
device 2, which applies predetermined voltages between ITOs 13 and
20. The light modulation portion 1A is configured from the AR coat
layer 22, the glass substrate 21, the ITO 20, the alignment layer
19, the liquid crystal layer 17, and the alignment layer 16.
As shown in FIG. 2, the SLM 1 with the above-described
configuration is arranged so that the thickness-direction of the
light modulation layer 17 is parallel with the Z axial direction
and so that the mirror layer 15 and the alignment layers 16, 19
extend parallel with the XY plane.
Next will be described, while referring to FIGS. 3A to 3D, how the
nematic liquid crystal is oriented in the light modulation layer
17. It should be noted that to improve clarity, FIGS. 3A to 3D show
only the AR coat layer 22, the alignment layer 19, the liquid
crystal layer 17, the alignment layer 16, and the reflection layer
15 of the SLM 1 in FIG. 2, and not the remaining layers 21, 20, and
14 to 11.
As shown in FIGS. 3A and 3B, in the light modulation layer 17, the
nematic liquid crystal molecules are oriented by the alignment
layers 16 and 19 to align in a horizontal or homogeneous posture in
parallel with the surfaces of the alignment layers 16 and 19 and to
face in a single predetermined direction "m". Described in more
detail, the long axes of the liquid crystal molecules are aligned
parallel to the surfaces of the alignment layers 16, 19, and face
in the predetermined direction "m". The long axes of the liquid
crystal molecules are arranged with no spiral structure with
respect to the thickness direction (Z direction) of the liquid
crystal layer 17. The predetermined direction "m" is determined by
the direction, in which the alignment layers 16 and 19 are
processed in rubbing or oblique deposition processes during the
production process of the SLM 1. According to the present
embodiment, the SLM 1 is located in the spatial light modulation
device 100 with the predetermined direction "m" facing parallel
with the Y axial direction (referred to as an SLM predetermined
reference position, hereinafter).
In this case, when a voltage is applied to the light modulation
layer 17 via the ITOs 13 and 20, then as shown in FIGS. 3C and 3D
the liquid crystal molecules are tilted or inclined to angles
within a plane that is parallel to the YZ plane that includes both
the predetermined direction "m" and the thickness direction Z of
the liquid crystal layer 17. It should be noted that a pretilt
configuration can be used, wherein the liquid crystal molecules are
originally tilted slightly within the plane parallel to the YZ
plane, even when no voltage is applied.
The liquid crystal in the light modulation layer 17 with this
parallel- or homogeneous- aligned configuration has birefringence.
For this reason, the SLM 1 controls birefringence by tilting the
liquid crystal molecules in accordance with voltage applied
thereto, and performs ECB (electrically-controlled birefringence)
type modulation. When the linearly-polarized light that falls
incident on the light modulation Layer 17 oscillates in a direction
which is twisted from the long axis of the liquid crystal
molecules, the oscillation plane will cross the long axis of the
liquid crystal molecules. As a result, phase difference is
generated, based on the difference in refractive indices, between
polarized light components that are parallel to the long axis of
the liquid crystal molecules and other polarized light components
that are perpendicular to the long axis of the liquid crystal
molecules. Accordingly, the plane of polarization of the
linearly-polarized light rotates. On the other hand, there will be
no rotation in the plane of polarization when the
linearly-polarized light that falls incident on the light
modulation layer 17 oscillates in a direction with no twist with
respect to the long axis of the liquid crystal molecules. In this
case, the linearly polarized light receives phase modulation based
on changes in the refractive index in the oscillation plane.
Accordingly, the linearly polarized light receives phase-only
modulation.
In the present embodiment, the liquid crystal molecules are
oriented to tilt within the plane parallel with the YZ plane, which
is the normal plane for the read light. Also, the light source 7
for the read light is disposed with an orientation that emits
P-polarized read light to the SLM 1. Because the oscillation plane
of the P-polarized read light is parallel with the YZ plane, no
twist exists between the long axis of the liquid crystal and the
oscillation plane of the read light that falls incident on the
liquid crystal layer. For this reason, the read light does not
cross the long axis of the liquid crystal molecules, and therefore
the plane of polarization of the read light does not rotate
Accordingly, high diffraction efficiency, can be achieved by
maintaining the polarization direction of the output light as the
P-polarized light.
Next, operation of the spatial light modulation device 100
according to the embodiment having the above-described
configuration will be described.
When the write light emitted from the light source 3 for write
light is transmitted through the liquid crystal television screen
5, predetermined image information controlled by the electric
signal generator 4 is written in the write light. The imaging lens
6 images the write light with this image information on the
photoconductive layer 14 of the SLM 1. The drive device 2 applies
an alternating current (AC) voltage of several volts between the
ITOs 13, 20 of the SLM 1. Electrical impedance at the
photoconductive layer 14 is changed by pixel positions in the write
light image. As a result, the light modulation layer 17 is applied
with a partial voltage whose amount changes individually for each
pixel. For this reason, the tilt of liquid crystal molecules also
changes according to the respective pixels. As shown in FIGS. 3C
and 3D, the liquid crystal molecules change their orientation
directions within the plane that is parallel with the YZ plane,
that is, the normal plane for the read light. As a result,
refractive index, with respect to the polarized light component
that oscillates within the normal plane (YZ plane), of the light
modulation layer 17, will change according to the respective
pixels.
Linearly-polarized light emitted from the He--Ne laser 7 is
adjusted into parallel light by the lens 8, the spatial filter 9,
and the collimator lens 10, and then input to the light modulation
layer 17 of the SLM 1 as P-polarized light. Because this read light
oscillates within a plane parallel with the normal plane, that is,
with the YZ plane, the read light propagates while being
phase-modulated by the changing refractive index in the light
modulation layer 17. This read light is reflected from the mirror
layer 15. The read light again propagates through the light
modulation layer 17, and is phase-modulated therein. The read light
then outputs from the light input surface 1a. At this time, the
phase modulation occurs with good efficiency because no plane of
polarization rotation occurs. The output read light is then Fourier
transformed by the Fourier transform lens 30A into a predetermined
Fourier transform image, for example, a hologram image and the
like. The Fourier transform image is formed on the Fourier
transform plane F.
In this way, according to the spatial light modulation device 100
of the present embodiment, the P-polarized light falls incident on
the reflection type spatial light modulator 1 as read light. The
liquid crystal molecules are oriented in a parallel or homogeneous
alignment so that they are tilted, in accordance with voltage
applied thereto by the drive circuit 2, within a plane in parallel
with the normal plane (YZ plane), that is, with a plane that
includes the optical axes of both of the modulated light (output
light) and the read light (input light). For this reason, during
light modulation, no rotation occurs in the plane of polarization
of the linearly-polarized light. Accordingly, high diffraction
efficiency can be obtained. High light usage efficiency can be
obtained. Also, because light is input to and reflected from the
SLM 1 at an angle, the input optical axis I is separated from the
output axis O. The optical system for input and output can be more
freely arranged and the efficiency of light usage can be increased
even further.
For comparison purposes, it is conceivable to modify the
orientation of the SLM I to an orientation (referred to as a "SLM
predetermined comparative position" hereinafter), shown in FIGS. 4,
5A, and 5B, by rotating the SLM 1 from the SLM predetermined
reference position around the Z axis by 90 degrees on the XY plane.
In this case, the predetermined direction "m", which is the
alignment direction of the long axes of the liquid crystal
molecules, becomes parallel with the X axial direction.
Accordingly, the long axes of the liquid crystal molecules are
oriented parallel with the XZ plane. When a voltage is applied to
the light modulation layer 17 in this situation, the long axes of
the liquid crystal molecules are tilted or inclined within a plane
that is parallel with the XZ plane as shown in FIGS. 5C and 5D.
Here, the XZ plane is perpendicular with the YZ plane, which is the
normal plane for the read light.
Further, as shown in FIG. 4, the light source of the read light 7
is rotated around the input optical axis I by 90 degrees from the
laser predetermined reference position to an orientation (which
will be referred to as a "laser predetermined comparative position"
hereinafter) so that the oscillation direction (polarization
direction) of the electric field in the read light will become
perpendicular with the normal plane (YZ plane). In this case,
the-read light falls incident on the light modulation layer 17 as
S-polarized light. When no voltage is applied, then as shown in
FIGS. 5A and 5B, the polarization direction of the read light is
parallel with the long axis direction of the liquid crystal
molecules. However, when a voltage is applied to the light
modulation layer 17, then as shown in FIGS. 5C and 5D, the liquid
crystal molecules are tilted at an angle within a plane parallel
with the XZ plane. As a result, twist develops between the
oscillation plane of the read light and the long axes of the liquid
crystal molecules, so that the oscillation plane of the read light
cuts across the liquid crystal molecules. For this reason, the
plane of polarization of the read light rotates so that a high
diffraction rate cannot be achieved.
The present inventors performed experiments to confirm the light
usage efficiency of the spatial light modulation device 100
according to the present embodiment. The results are indicated
below.
FIRST EXPERIMENT
First, a comparative experiment was performed as a first experiment
in order to confirm improvement in light usage efficiency of the
spatial light modulation device 100 of the present embodiment
In this experiment, a vertical stripe image was displayed on the
liquid crystal television 5 in the spatial light modulation device
100 with the configuration shown in FIG. 1. Change was measured in
the diffraction efficiency (intensity ratio of a first order
diffraction light of the read light emitted from the SLM 1) that
occurred when the number of displayed stripes (spatial frequency)
was changed and when the angle of incidence .theta. of the read
light was changed. During the experiment, in accordance with the
configuration of the present embodiment, the SLM 1 was arranged in
the SLM predetermined reference position, that is, in the
orientation shown in FIGS. 3A to 3D, so that the liquid crystal
molecules were tilted within a plane parallel with the normal plane
(YZ plane) for the read light. The laser light source 7 was
disposed in the laser predetermined reference position, that is,
the orientation shown in FIGS. 1 and 3A to 3D, so that the
oscillation plane of the read light was parallel with the normal
plane, that is, with the YZ plane. Accordingly, the read light fell
incident on the SLM 1 as P-polarized light.
Also, as a comparative example, the SLM 1 was disposed in the SLM
predetermined comparative position, that is, in the orientation
shown in FIGS. 5A to 5D, so that liquid crystal molecules were
tilted within the plane parallel with a plane (XZ plane)
perpendicular to the normal plane (YZ plane) for the read light.
The laser light source 7 was disposed in the laser predetermined
comparative position, that is, in the orientation shown in FIGS. 4,
and 5A to 5D, so that the oscillation plane of the read light was
oriented perpendicular to the normal plane, that is, the YZ plane.
Accordingly, the read light fell incident on the SLM 1 as
S-polarized light.
FIG. 6 shows experiment results of the diffraction efficiency
obtained using the arrangement of the present embodiment. FIG. 7
shows experiment results of diffraction efficiency obtained using
the arrangement of the comparative example.
It was confirmed that using the arrangement of the comparative
example, the diffraction efficiency drops with increase in the size
of the incident angle .theta.. In contrast, according to the
arrangement of the present embodiment, the diffraction efficiency
is maintained high for all the different incident angles .theta..
It can be understood that according to the present embodiment, the
incident angle .theta. can be increased while maintaining a high
diffraction efficiency, that is, a high efficiency of light usage.
It is confirmed that by using the arrangement of the present
embodiment, even when the read light falls incident on the input
surface at an angle, no rotation occurs in the plane of
polarization of the modulation light, and therefore high
diffraction efficiency, that is, high efficiency of light usage,
can be obtained in the same degree as when the read light is
inputted normal to the input surface.
According to the present embodiment, because the incident angle
.theta. can be increased while maintaining a high diffraction
efficiency, that is, a high efficiency of light usage, the input
light path I and the output light path O of the read light can be
completely separated from each other without use of additional
optical members, such as a half mirror. Therefore, the present
embodiment has the additional merit of increasing the freedom of
design for the input optical path I and the output optical path O
while obtaining a high light usage efficiency.
SECOND EXPERIMENT
Further, the present inventors performed a second experiment.
In this experiment, the positions of the SLM 1 and the laser light
source 7 were maintained in the conditions of the present
embodiment of FIG. 1, and the normal plane for the read light was
maintained fixed on the YZ plane. While maintaining these
conditions, the orientation of the light source 7 of the read
light, that is, the light polarization direction of the read light,
was rotated around the input light optical axis I and, at the same
time, the orientation of the SLM 1 was rotated around the Z axis,
thereby changing the ratios of the S-polarized light component and
of the P-polarized light component of the read light that falls
incident on the SLM 1. How the diffraction efficiency changed in
association with changes in ratio of the polarized light components
was measured.
Here, the ratio of the P-polarized light component to the
S-polarized light component can be made to a desirable ratio of
"a:1-a" (where the ratio of the P-polarized light component is "a",
and the ratio of the S-polarized light is "1-a", wherein
0.ltoreq.a.ltoreq.1) by, as shown in FIG. 8, shifting the
orientation of the laser light source 7 by an angle .alpha. (=arc
tan[(1-a)/a]).sup.1/2) from the laser predetermined reference
position, that is, from the orientation wherein the read light
oscillation plane is within the YZ plane. At the same time, the
orientation of the SLM 1 is also changed by the same angle .alpha.
from the SLM predetermined reference position, that is, the
orientation wherein the liquid crystal arrangement direction "m"
extends in the Y axis direction, in order to maintain that no twist
exists between the read light oscillation plane and the liquid
crystal arrangement direction "m" of the SLM 1.
For example, it can be understood that in order to set the ratio of
P-polarized light component to S-polarized light component to 1:0,
the SLM 1 and the laser light source 7 should be disposed at the
SLM predetermined reference position and the laser predetermined
reference position, respectively, because .alpha.=0.degree. (=arc
tan [0/1].sup.1/2) can be determined by knowing that a=1.
Also, in order to set the ratio of the P-polarized light component
to S-polarized light component to 0.9:0.1, the SLM 1 and the laser
light source 7 should be disposed with an orientation shifted by an
angle .alpha. of 18.46.degree. from the SLM predetermined reference
position and the laser predetermined reference position,
respectively, because .alpha.=18.4.degree. (=arc tan
[0.1/0.9].sup.1/2) can be determined by knowing that a=0.9.
Further, in order to set the ratio of P-polarized light component
to the S-polarized light component to 0:1, the SLM 1 and the laser
light source 7 should be disposed with an orientation shifted by an
angle .alpha. of 90.degree. from the SLM predetermined reference
position and the laser predetermined reference position,
respectively, because .alpha.=90.degree. (=arc tan [1/0].sup.1/2)
can be determined by knowing that a=0. In this case, the SLM 1 and
the laser light source 7 are disposed at the SLM predetermined
comparative position and the laser predetermined comparative
position (FIGS. 4 and 5A to 5D), respectively.
The initial arrangement for the experiment was with the laser light
source 7 oriented in the laser predetermined reference position,
that is, .alpha.=0.degree., as indicated by the solid line in FIG.
8, so that the plane of polarization is parallel with the YZ plane.
Also, the SLM 1 was disposed with orientation of the SLM
predetermined reference position (.alpha.=0.degree.) so that liquid
crystals were arranged with direction "m" in parallel with the Y
axis direction. In this situation, the ratio "a" of P-polarized
light component was 1, so that read light with 100% P-polarized
light component fell incident on the SLM 1.
While in this reference position, a binary phase grating was formed
on the SLM 1 and the SLM 1 was driven using a drive voltage of 3.0
[V] and at an oscillation of 1 [kHz]. The diffraction efficiency
was measured. It should be noted that the incident angle .theta. of
the input optical axis I was set at 15.degree.. Also, the drive
voltage was changed to 4.0 [V] and the same measurements were again
performed.
Next, in order to set the ratio of P-polarized light to S-polarized
light to 0.9:0.1 (that is, a=0.9), the laser light source 7 was
rotated clockwise (looking at the laser light source 7 on the input
optical axis I from behind the laser light source 7) around the
input optical axis I. As a result, as indicated in dotted line in
FIG. 8, the light source 7 was oriented with an angular shift from
the laser predetermined reference position by a predetermined angle
.alpha.=18.4.degree.. The SLM 1 was rotated around the Z axis in
the clockwise direction (looking at the input surface 1a of the SLM
1 from above along the Z axis) by an angle equivalent to that of
the laser light source 7, which placed the SLM 1 in an orientation
shifted from the SLM predetermined reference position by the same
predetermined angle .alpha.=18.4.degree.. As a result, read light
with 90% P-polarized light component and the remaining 10%
S-polarized light component fell incident on the SLM 1. The
diffraction efficiency was again measured in this condition.
The same diffraction efficiency measurements as described above
were repeatedly performed while decreasing the ratio "a" of the
P-polarized light in the read light by 0.1 increments. That is,
measurements were repeatedly performed while gradually increasing
the angle .alpha. of the SLM 1 from the SLM predetermined reference
position, and the angle .alpha. of the laser light source 7 from
the laser predetermined reference position, in accordance with the
P-polarized light ratio value "a".
Once the SLM 1 and the laser light source 7 reached the SLM
predetermined comparative position and the laser predetermined
comparative position (.alpha.=90.degree.), measurements were
performed. At this time, the ratio "a" of the P-polarized light
component was zero (0), so that read light formed from 100%
S-polarized light component fell incident on the SLM 1. Thus, the
present experiment was completed for the incident angle .theta. of
the input optical axis I of 15.degree..
The same experiments as described above were again performed after
changing the incident angle .theta. of the input optical axis I to
30.degree..
Results of measuring the diffraction efficiency are showing in FIG.
9, wherein the horizontal axis indicates the ratios of P- and
S-polarized components and the vertical axis indicates the
diffraction efficiency.
As is clear from the measurement results, it was confirmed that an
extremely high diffraction efficiency could be obtained at the
predetermined reference position (.alpha.=0.degree.), wherein the
read light is formed from 100% P-polarized light component,
independent of the size of the incident angle .theta. and the drive
voltage.
Also, it was confirmed that sufficiently high diffraction
efficiency could be obtained when the read light was not 100%
P-polarized light but included approximately 100% P-polarized
light. For example, it can be understood that sufficiently high
diffraction efficiency can be obtained regardless of the size of
the incident angle .theta. and the drive voltage, if the ratio of
P-polarized light is greater than or equal to 0.9 and smaller than
or equal to 1, that is, when the P-polarized light component is
greater than or equal to 90% and smaller than or equal to 100%, and
the S-polarized light is greater than or equal to 0% and smaller
than or equal to 10%. In concrete terms, it can be understood that
sufficiently high diffraction efficiency can be obtained even if
the orientation of the laser light: source 7 shifts from the
predetermined reference position by an angle greater than or equal
to 0.degree. and smaller than or equal to 18.4.degree., and the
orientation of the SLM 1 shifts from the predetermined reference
position by an angle greater than or equal to 0.degree. and smaller
than or equal to 18.4.degree..
Said differently, the polarization direction of the read light need
not be completely (100%) parallel with the normal plane (YZ plane)
for the read light. The polarization plane of the read light need
only be within a plane that is approximately 100% parallel with the
normal plane (YZ plane) for the read light, for example, within a
plane that is shifted, by an angle greater than or equal to
0.degree. and smaller than or equal to 18.4.degree., from the
normal plane (YZ plane) for the read light. Also, the SLM 1 need
not be arranged so that the liquid crystal molecules will tilt or
incline within a plane that is completely (100%) within the normal
plane (YZ plane) for the read light. The liquid crystal molecules
need only be arranged to tilt within a plane that is approximately
100% parallel with the normal plane (YZ plane) for the read light,
for example, within a plane that is shifted, by an angle greater
than or equal to 0.degree. and smaller than or equal to
18.4.degree., from the normal plane (YZ plane) for the read
light.
The spatial light modulation device 100 of the present embodiment
having the above characteristics can be used, for example, in image
displays, optical analog calculators, and the like, and also in
laser processing devices and the like. A laser processing device is
for converging light on a work piece, such as a metal plate, to cut
or laser-mark the work piece.
When the spatial light modulation device 100 of the present
embodiment is used in a laser processing device, a YAG laser, for
example, can be used as the light source 7 of the read light
instead of a Re--Ne laser. The work piece can be processed by
converging laser light into a desired pattern (Fourier pattern) on
a work piece that is positioned on the Fourier transform plane F.
Described in more detail, an image such as a hologram is formed on
the SLM 1 using the liquid crystal television 5. As per FIGS. 1 and
3A to 3D, read light of P-polarized light falls incident at a slant
on the SLM 1. The P-polarized read light receives phase modulation
that corresponds to the inputted pattern, and is Fourier
transformed by the Fourier transform lens 30. By this, the read
light converges in the desired pattern on the work piece so that
the work piece is processed.
There is very little loss of read light, because the read light
falls incident on the SLM 1 at a slant and therefore no half mirror
is used for separating the input optical axis from the reflection
optical axis. Furthermore, the read light can be converged into the
desired pattern with high diffraction efficiency, because only the
phase of the read light is modulated. For this reason, the read
light from the light source 7 of the read light can be efficiently
used in processing.
It should be noted that the read light can have approximately 100%
P-polarized light component, and need not be 100% P-polarized light
component. Also, the SLM 1 may be oriented so that the plane,
within which the liquid crystal molecules of the SLM 1 tilt in
association with application of voltage, be approximately parallel
with, and need not be completely parallel with, the normal plane
(YZ plane) for the read light.
Normally, heat from components in the laser source causes
deformation, so that the wave front of the light emitted from the
laser 7 becomes distorted and does not become a completely parallel
beam. In this case, the converged spot becomes larger so that the
precision of processing drops. Because broadening of the converged
spot is associated with decrease in power density, it is also
associated with inability to efficiently process.
FIG. 10 shows a laser processor 200, which is a modification of the
spatial light modulation device 100 of the embodiment. In order to
form a complete parallel light, the laser processor 200 can correct
the wave front of laser light that has been distorted for the
above-described reasons.
The configuration of the laser processor 200 is substantially the
same as that of the spatial light modulation device 100 of the
embodiment shown in FIG. 1, but differs in that a beam splitter 36
is provided on the input optical axis I at a position between the
SLM 1 and the collimator lens 10. The beam splitter 36 is for
guiding a portion of the read light to the SLM 1 and another
portion of the light to a wave front detection device 35. The wave
front detection device 35 is configured from an interference
system, or a Hartmann sensor that uses a micro lens array. The wave
front detection device 35 measures the amount of distortion in the
wave front of laser light from the beam splitter 36. The wave front
detection device 35 is connected to the electric signal generator 4
and, based on the measurement results, controls the electric signal
generator 4 to produce a phase pattern for correcting the wave
front of the read light to produce an output light of a desired
plane wave. For this reason, the SLM 1 can adjust phase of the read
light and can produce output light with a plane wave front. Because
the output light subjected to Fourier transform at the Fourier
transform lens 30 has a plane wave front, a smaller spot can be
formed on the work piece 37, which is positioned on the Fourier
transform plane F. Laser processing can be achieved with higher
precision. It should be noted that the read light in the laser
processing device 200 also can be approximately 100% P-polarized
light component and need not have completely 100% P-polarized light
component. Also, the orientation of the SLM 1 can be arranged so
that the plane within which the liquid crystal molecules tilt in
association with application of voltage be approximately parallel
with, and need not be completely parallel with, the normal plane
(YZ plane) for the read light.
FIG. 11 is a schematic view showing another example of an
application of the spatial light modulation device 100 in the
present embodiment.
In this example, the spatial light modulation device 100 is applied
to an optical interconnection device 60. The optical
interconnection device 60 is for switching connection of elements
between parallel computation boards 40 and 50, which exchange
information using light.
The parallel computation board 40 includes a light receiving
element array 41 for information input and a laser diode array 42
for information output. The parallel computation board 50 includes
a light receiving element array 51 for information input and a
laser diode array 52 for information output. The optical
interconnection device 60 is disposed between the laser diode array
42 of the parallel computation board 40 and the light receiving
element array 51 of the parallel computation board 50.
The configuration of the optical interconnection device 60 is
substantially the same as the configuration of the spatial light
modulation device 100 of the embodiment shown in FIG. 1, but
differs in that the read light optical system of the optical
interconnection device 60 includes a prism 61 and a Fourier
transform lens 30' in place of the laser light source 7, the lens
8, the spatial filter 9, the collimator lens 10, and the Fourier
transform lens 30. The prism 61 is for reflecting read light
emitted from the laser diode array 42. The Fourier transform lens
30' is for performing a Fourier transform on the read light
reflected from the prism 61 and inputting the read light into the
read light input surface 1a of the SLM 1. The Fourier transform
lens 30' further serves to again perform a Fourier transform
operation on the read light that has been output from the read
light output surface 1a after modulation by the SLM 1. It should be
noted that the prism 61 serves to reflect the read light that has
been output from the Fourier transform lens 30' and to guide the
light to the light receiving element array 51.
The SLM 1 is disposed at the predetermined reference position
(FIGS. 1 to 3D). The line normal to the mirror layer 15 is parallel
with the Z axis. Moreover, the liquid crystal molecules in the
liquid crystal layer (FIG. 2) tilt or incline within a plane that
is parallel with the YZ plane. Also, the read light emitted from
the laser diode array 42 and reflected from the prism 61 propagates
following the YZ plane, falls incident on the read light input
surface 1a at a slant (at an angle .theta.), reflects off the
mirror layer 15, again propagates following the YZ plane, and
returns to the prism 61. That is, the YZ plane is the normal plane
for the read light. Further, the laser diode array 42 emits read
light that is linearly polarized. The laser diode array 42 is
disposed in an orientation so that it emits P-polarized light whose
plane of polarization is parallel with the YZ plane.
It should be noted that the light source 3, the transmission type
liquid crystal television 5 for displaying the write image, and the
imaging lens 6 are disposed on the write light input surface 1b
side of the SLM 1 in the same manner as in the arrangement of FIG.
1. The liquid crystal television 5 is connected to the electrical
signal generator 4 which serves as a write image controller.
In the optical interconnection device 60 with this configuration,
the control unit 4 controls the liquid crystal television 5 to
display a hologram pattern for optical path switching. When the
write light emitted from the light source 3 passes through the
liquid crystal television 5, the light path switching hologram
pattern is written on the write light. The write light written with
this hologram pattern is imaged, via the imaging lens 6 on the
photoconductive layer 14 (FIG. 2) of the SLM 1.
The output signal from the parallel computation board 40 is output
by the laser diode array 42 as two-dimensional or one-dimensional
image information. The image is reflected from the prism 61 and
guided to the SLM 1 via the Fourier transform lens 30' as the read
light. Then, the read light is input into the light modulation
layer 17 of the SLM 1. The read light receives a predetermined
phase modulation according to the optical path switch hologram
pattern imaged on the photoconductive layer 14. The modulated image
again passes through the Fourier transform lens 30', reflects off
the prism 61, and outputs to the light receiving element array 51
of the parallel computation board 50.
By changing the hologram image displayed on the liquid crystal
television 5, the connection can be switched between optional
pixels pairs in the laser diode array 42 of the parallel
computation board 40 and in the light receiving element array 51 of
the parallel computation board 50.
In the optical interconnection device 60 also, P-polarized
linearly-polarized light, wherein the plane of polarization is
parallel with the normal plane, is used as the read light.
Moreover, the orientation of the SLM 1 is disposed at the
predetermined reference position and the plane in which the liquid
crystal molecules tilt in association with application of voltage
is set to be parallel with the normal plane of the read light. This
can obtain high diffraction efficiency. Accordingly, the parallel
computation boards 40, 50 can be reliably connected,
It should be noted that in the optical interconnection device 60
also, the read light can have approximately 100% P-polarized light
component and need not be 100% P-polarized light component. Also,
the orientation of the SLM 1 need only bring the plane, in which
the liquid crystal molecules tilt in association with application
of voltage, into approximately parallel relation with, and not 100%
parallel relation with, the read light normal plane (YZ plane).
Next, the spatial light modulation device 100 according to a second
embodiment of the present invention will be explained.
The spatial light modulation device 100 of the present embodiment
has substantially the same configuration as the spatial light
modulation device 100 of the first embodiment shown in FIG. 1,
except that it uses an optically addressed type homeotropic
arrangement liquid crystal spatial light modulator as the SLM 1 in
place of the optically addressed type parallel alignment liquid
crystal spatial light modulator. More specifically, the SLM 1 and
the light source 7 of the read light are arranged so that the
normal plane for the read light matches the YZ plane. Also, the
read light source 7 is arranged so that the plane of polarization
is parallel with the YZ plane, that is, so that p-polarized read
light fall incident on the liquid crystal layer 17.
The homeotropic arrangement liquid crystal spatial light modulator
has the same configuration shown in FIG. 2 for the parallel
arrangement liquid crystal spatial light modulator. However, the
liquid crystal layer 17 is homeotropic arrangement processed by the
alignment layers 16, 19 as shown in FIGS. 12A and 12B. That is, the
long axis of the liquid crystals is oriented perpendicular with the
surface of the alignment layers 16, 19. When a voltage is applied
to the liquid crystal layer 17, then as shown in FIGS. 12C and 12D
the liquid crystal molecules tilt or incline within a plane that is
parallel with a plane including the depth direction (Z axis) of the
liquid crystal layer 17 and a single predetermined direction "m".
The predetermined direction "m" is determined by the process
direction, in which the alignment layers 16, 19 are processed in
the rubbing or oblique deposition processes during the production
process of the SLM 1. In the case of the present embodiment, when
arranging the SLM 1 in the spatial light modulation device 100, the
predetermined direction "m" of the SLM 1 is aligned in parallel
with the Y axial direction, that is, the SLM 1 is placed at the
predetermined reference position. Accordingly, the liquid crystal
molecules tilt within a plane that is parallel with the YZ plane.
It should be noted that a pretilt configuration can be used,
wherein the liquid crystal molecules are originally tilted slightly
within the plane parallel with the YZ plane even when no voltage is
being applied.
With the configuration of the present embodiment, even if the
liquid crystal molecules tilt within the plane that is parallel
with the YZ plane, the read light falls incident without crossing
the liquid crystal molecules because no twist is developed between
the liquid crystal molecules and P-polarized light that oscillates
within the plane that is parallel with the YZ plane. Accordingly,
phase-only modulation can be reliably achieved without any rotation
of the polarization plane of the read light, so high diffraction
efficiency can be achieved.
In this way, the spatial light modulation device of the present
embodiment uses P-polarized light input at a slant in the read
light, and the liquid crystal molecules in the light modulation
layer 17 of the SLM 1 are oriented in the homeotropic arrangement
so as to tilt, in association with the application of a voltage,
within the plane that is parallel with the normal plane (YZ plane)
of the read light, Therefore, the polarization plane of the light
does not rotate during light modulation. Accordingly, high
diffraction efficiency can be obtained and high usage efficiency
can be obtained. Also, because the light is reflected off the SLM 1
at a slant, the input optical axis and the output optical axis can
be separated from each other. The arrangement of the input and
output optical systems have higher freedom of design and usage
efficiency of light increases still further.
It should be noted that in the same way as in the first embodiment,
the read light need only have approximately 100% P-polarized light
component, and need not be completely 100% P-polarized light. Also,
the orientation of the SLM 1 need only be so that the plane in
which the liquid crystal molecules tilt in association with
application of voltage is approximately parallel with, and need not
completely parallel with, the normal plane (YZ plane) of the read
light.
The spatial light modulation device 100 of the present embodiment
can be used in a laser processing unit, an optical connection
device, and the like in the same way as the first embodiment.
The spatial light modulation device of the present invention can be
modified in a variety of ways, and is not limited to the
above-described embodiments.
For example, a variety of types of laser source can be used as the
light source of the read light, in order to output
linearly-polarized read light.
Also, the orientation of the liquid crystal is not limited to the
homogeneous arrangement shown in FIGS. 3A to 3D nor to the
homeotropic arrangement shown in FIGS. 12A to 12D, but could be a
hybrid arrangement or a slanted or tilted arrangement. It is
sufficient that the liquid crystal molecules be arranged so that
when a voltage is applied, they will tilt within the plane that is
approximately parallel with the normal plane of the read light.
Further, an optically addressed type spatial light modulator is
used in the above embodiment as the SLM 1. However an electrically
addressed type spatial light modulator could be used instead. In
this case, an electrode array with a plurality of pixel electrodes
is provided in place of the ITO 13 and the photoconductive layer 14
in the optical address portion 1B. By selectively applying image
signals to the individual electrodes, the voltage applied to the
liquid crystal layer 17 can be controlled separately for each
pixel.
Further, a variety of different types of transmission type
electrically addressed type spatial light modulators can be used
instead of the transmission type liquid crystal television 5.
INDUSTRIAL APPLICABILITY
The spatial light modulation device according to the present
invention can be broadly used in a variety of spatial light
modulation devices that use phase modulation. For example, it can
be used broadly for laser processing, optical computing, computer
generated holograms, and the like.
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